earthworm biohumus conditioning for pellet...

ENGINEERING FOR RURAL DEVELOPMENT Jelgava, 25.-27.05.2016.

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EARTHWORM BIOHUMUS CONDITIONING FOR PELLET PRODUCTION

Olafs Vronskis1, Aaivars Kakitis

1, Egils Laukmanis

2, Imants Nulle

1

1Latvia University of Agricultrure;

2SIA Bioorganic Earthworm Compost, Latvia

[email protected], [email protected], [email protected], [email protected]

Abstract. Vermicomposting is widely being used for bio-conversion of organic wastes into bio-fertilizers

through the use of worms, bacteria, and fungi. By managing vermicomposting we are essentially speeding up the

natural process of breaking down organic matter. In Latvia, vermicompost has been applied as a bio-fertilizer in

its raw form. This has challenges in terms of storage and packaging for sale, especially when there is mass

production of vermicompost. This study therefore focused on the suitable technologies of pelleting

vermicompost in small and medium scale vermicomposting farms. Experiments to determine the moisture

content of SIA Bioorganic Earthworm Compost biohumus were carried out. Vermicompost pelleting process

parameters depending on the moisture content were investigated. Total moisture content of vermicompost is in

the range of 42…51 %. Bulk density of vermicompost pellets (diameter 6 mm) is 750-780 ± 20 kg·m-3

.

Keywords: vermicompost, pellets, density, moisture content.

Introduction

Vermicomposting is a special type of composting, which uses certain earth worms. The

earthworm species most often used are Red Wigglers. These species are only rarely found in soil and

are adapted to special conditions in rotting vegetation, compost and manure piles.

Vermicompost is a bio-fertiliser that is obtained from bio-conversion of organic waste.

Vermicompost is the end-product of breakdown of organic matter by some species of earthworms.

Vermicompost is a nutrient-rich, natural fertilizer and soil conditioner.

The benefits of vermicompost to seedling vigour and plant health are attributed in large part to

high concentrations of plant available macro- and micro nutrients, plant growth promoting organic

acids and high microbial activity, all of which may confer tolerance to stress [1].

The possible compaction of these composted solids into pellets further homogenizes and

dehydrates their organic matter enhancing. Its uniformity and fertilizing properties as well as

densification, such as pelleting, is a solution for these problems, which increase the bulk density,

improve storability, reduce transportation costs and make these materials easier to handle [2].

Vermicompost (VC), which is produced by the fragmentation of organic wastes by earthworms,

contains nutrients in forms that are readily available for plant uptake [3].

SIA Bioorganic Earthworm Compost produces high quality earthworm compost or biohumus

using the technology VERMIC 3.5 acquired in Austria (Fig. 1). The raw materials for compost, which

is fed to the earthworms, come from clean, unpolluted surroundings, superiorly from organic certified

farmers. Compounds are composed of cattle manure, green grass, mainly lucerne (alfalfa) and straw.

Fig. 1. Ltd Bioorganic Earthworm Compost (source: http://www.bioec.lv)

Biohumuss is widely used for production of various vegetables. However, its use is difficult in

places such as recreation, sports, golf, and football fields. Humus uneven distribution across the field

promotes grass growth at different speeds. The result is not acceptable. Therefore, to develop

vermicomposting end product usability there is a need to work in several directions.

One of the directions is to develop the possibility of humus evenly spreading across the field, to

develop a new or improve the existing technology, which allows doing it with minimal impact on the

product quality.


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Granular vermicompost can be called concentrated fertilizer, because the recycling process

reduces the volume of material more than 10 times, due to water removal and material thickening

while extruding [4].

When transporting it larger distances and storing, it is desirable that the moisture content is

minimal, because it affects both the mass of the products, as well as microbial activity. It is therefore

necessary to examine the humus moisture content and determine the energy needed for drying it.

The density of the product also improves transport efficiency, so the solution could be

vermicompost granulation. Pellets are easier to be dosed and spread on the field.

In cooperation with the company Ltd. Bioorganic Earthworm Compost discussions about the

appropriate granulation technology for medium-sized company took place. Therefore, in this article

possible vermicompost granulation technologies and their advantages and disadvantages will be

analysed.

Materials and methods

In the experiment natural vermicompost was used. Moisture content of vermicompost used in the

sieve analysis was ~4 %, but density 264 kg·m-3

. Sieve analysis (according to LVS EN 15149-1)

showed that there are just 1 % particles that did not pass through the sieve with the hole diameter

3 mm (Fig. 2).

Visual estimation of particles (Fig. 3) let us state that dried vermicomopost is a homogenous

material. Just in finer particles some small grains of sand – white colour – can be detected.

Fig. 2. Particle size distribution of vermicompost

Fig. 3. Vermicompost particles after sieve analysis

Granulation experiments let us evaluete the quality (density, moisture content) of pellets, the

required moisture of vermicompost and temperature in the pelleting process. Granulation was carried

out with the small scale 4 kW flat die granulator ZLSP150B for sawdust granulation (Fig. 4).


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Fig. 4. Flat die extrusion granulator ZLSP150B

Vermicompost with different moisture content was granulated. The particle density of pellets and

the moisture content (according to LVS EN 14774) as well as the bulk density of pellets (according to

LVS EN 15103) were determined.

The diameter and length of 21 pellets from each sample were measured by a digital caliper. The

corresponding mass of a pellet was also obtained with a digital balance with an accuracy of 0.01 g.

Particle density was calculated as mass and volume proportion.

Results and discussion

For humus granulation more frequently used granulator types are shown in Table 1. This table

summarizes the advantages and disadvantages of granulators.

Overall, less investments are necessary for the use of the disc and flat die granulator. If we

compare these two, from the point of view of the naturalness of the product, the disk granulator is

preferred as flat die granulator in the granulation process on the die surface with high temperature. In

our experiment we measured the die temperature 90...95 ºC. Temperature of the pellets in the

granulator outlet was 70…80 ºC.

The moisture content of pellets must be less than 20 % [2]. Deterioration of pellets during the

storage period is important in order to keep the quality of the compost. More molds generate on the

surface of compost pellets than ordinary compost with the same moisture content. It is advised to

reduce the moisture content of the pellets to 15 % or less, because deterioration by condensation is

caused even at 20 % moisture content [2].

Total moisture content (on wet basis) of vermicompost determined with the oven dry method is in

the range of 42…51 %.


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Table 1

Types of granulators

No Type of granulator Notes

1

Drum granulator

Source: www.alibaba.com

Advantages:

• High productivity, durable;

• Easy adjustment;

• Minimum maintenance.

Disadvantages:

• Big dimensions and weight [6; 7].

2

Disk granulator

Source: www.feeco.com

Advantages:

• Compactness;

• Economical;

• Possibility of obtaining the required size pellets.

Disadvantages:

• Productivity depends on the equipment size [6].

3

Flat die extrusion granulator

Source:www.buskirkeng.com

Advantages:

• Compactness;

• Economical;

Disadvantages:

• Increased working parts wane;

• Time-consuming work of parts replacement [5; 6].

4

Ring Die Pellet Mills

Source: www.stolz.fr

Advantages:

• Compactness;

• High productivity;

Disadvantages:

• Increased working parts wane;

• Time-consuming work of parts replacement [5; 6].

5

Double roller extrusion

granulator

Source: www.longerinc.com

Advantages:

• Compactness;


Disadvantages:

• Time-consuming work of parts replacement.

6

Combined flat die and two

disc granulators

www.fertilizer-machine.net

Advantages:


• Protecting bacteria at room temperature, smooth

granulating path inside the granulating machine.

Disadvantages:

• Big dimensions and weight;

• Increased working parts wane.


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The pelleted organic compost fertilizer pellet moisture content was 15-20 % (Fig. 5). If the

moisture content is 20 %, in the pelletizing process approximately 5 % moisture evaporates, when the

humidity of the mass is higher the volatile water content also will be higher (Fig. 5). The pellet bulk

density was influenced by the vermicompost moisture.

Fig. 5. Moisture content before and after granulation

Determined bulk density of vermicompost pellets (diameter 6 mm) in dependence on the moisture

content (20, 24, 27 %) was 750-780 ± 20 kg·m-3

(Fig. 6). It can be concluded that the pellet density is

higher if the mass moisture content is lower than 20 %.

Fig. 6. Bulk density of pellets

The obtained particle density of vermicompost pellets in dependence on the moisture content (20,

24, 27 %) was 1480-1600 ± 15 kg·m-3

(Fig. 7).

In this study a sawdust pellet mill was used and the flat die surface temperature reached

95 degrees. The study should be continued to investigate the granulated vermicompost fertilizer

efficiency after processing at high temperature.


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Fig. 7. Pellet particle density

Conclusions

1. Total moisture content (on wet basis) of vermicompost determined with the oven dry method is in

the range of 42…51 %.

2. Less investments are necessary for the use of the disc and flat die granulator.

3. Disk granulator is recommended instead of the flat die granulator, because in the granulation

process on the die surface is high temperature (90 ... 95 ºC).

4. In the pelletizing process approximately 5 % moisture evaporates, if the initial moisture content is

20 %.

5. Bulk density of vermicompost pellets (diameter 6mm) is 750-780 ± 20 kg·m-3

.

6. Particle density of vermicompost pellets in dependence on the moisture content is in the range of

1480-1600 ± 15 kg·m-3

.

References

1. Arancon N.Q., Edwards C.A., Atiyeh R. and Metzger J.D. Effects of vermicomposts produced

from food waste on the growth and yields of greenhouse peppers. Elsevier Journal, vol. 93,

“Bioresources Technology”, 2004, pp. 139-144.

2. Absalan G., Kianmehr M.H., Arabhosseini A. and Kouravand S. Optimization compressive

strength biomass pellet from compost using Taguchi method. CIGR Journal, vol. 17(1),

“Agricultural Engineering International”, 2015, pp. 166-172.

3. Atiyeh R.M., Subler S., Edwards C.A., Bachman G., Metzger J.D., and Shuster W., 2000. Effects

of vermicompost and composts on plant growth in horticultural container media and soil. Pedo

Biologia, 44, 579-590. [online] [28.10.2015.]. Available at: http://ejuz.lv/8gr

4. Pocius A., Jotautiene E., Mieldazys R., Jasinskas A., Kucinskas V. Investigation of granulation

process parameters inf luence on granulated fertilizer compost properties. Proceedings of 13th

International Conference “Engineering for Rural Development”, 2014, pp. 407-412.

5. Жигжитов А.В. Механизация процессов консервирования и приготовления кормов (The

mechanization of the processes of preservation and preparation of feed). Улан-Удэ: БГСХА им.

В.Р. Филиппова, 2008. 105 с (in Russian).

6. Классен П.В., Гришаев И.Г. Основы техники гранулирования (Basics of granulation

technology). Москва: Химия, 1982. 272 с (in Russian).

7. Першин В.Ф. Переработка сыпучих материалов в машинах барабанного типа (Processing

of bulk materials in drum-type machines). Москва: Машиностроение, 2009. 216 c (in Russian).

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